The present application relates to an optical measuring device for identifying a sample such as minute particles flowing in a channel, and more particularly to a technique for identifying the kind etc. of the sample by detecting fluorescence generated from the sample irradiated with laser light having a specific wavelength.
In the case of identifying biological minute particles such as cells, microorganisms, and ribosomes, an optical measuring method using flow cytometry (flow cytometer) is generally used (see Hiromitsu Nakauchi, supervisor, “Cell Engineering Separate Volume, Experimental Protocol Series, Flow Cytometry Jiyujizai,” Second Ed., Shujunsha Co., Ltd (Aug. 31, 2006), for example). The flow cytometry is a method of individually identifying a plurality of minute particles flowing in a line in a channel by applying laser light having a specific wavelength to the minute particles and detecting fluorescence or scattered light generated from each minute particle irradiated with the laser light.
More specifically, a sample liquid containing a plurality of minute particles as an object to be measured and a sheath liquid flowing around the sample liquid form a laminar flow in a flow cell to line the minute particles contained in the sample liquid. In this condition, laser light is applied to the flow cell, so that the minute particles are individually passed through the laser beam. At this time, each minute particle is excited by the laser light to generate fluorescence and/or scattered light, which are/is next detected by using a photodetector such as a CCD (Charge Coupled Device) or a PMT (Photo-Multiplier Tube). The light detected by the photodetector is converted into an electrical signal and digitized to perform statistical analysis, thereby determining the kind, size, structure, etc. of each minute particle.
In related art, proposed is a flow cytometer using a multichannel photodetector having a plurality of detection channels, such as a multianode photomultiplier tube (see U.S. Pat. No. 7,280,204 (hereinafter referred to as Patent Document 1) and Japanese Patent Laid-open No. Hei 5-10946 (hereinafter referred to as Patent Document 2), for example). Such an existing flow cytometer using a multichannel photodetector as described in Patent Documents 1 and 2 can simultaneously measure a plurality of light beams having different wavelengths. In the device described in Patent Document 2, a multianode photomultiplier tube is used as a photodetector to detect light intensity at each detection channel by counting photons, thereby improving the detectivity and reproducibility.